The present invention relates to a monitoring circuit for control means and selective breakaway means in modular power supply systems, particularly for telecommunications equipment. More particularly, the present application relates to a circuit designed to enable the right distribution of the load among the elements which compose the system as well as the location and the selective switching off of the units that are out of order. The supply systems of the type described above are usually comprised of a plurality of basic unit (such as rectifiers, or inverters, etc.) that are connected to each other in parallel. This type of connection is used, for example, when the power to be supplied by the system is not delivered by a single power unit and the power is therefore supplied by several power units that are connected in parallel to each other. In addition to the power units that are necessary to supply the operating power, usually at least one other power unit is added, in order to act as a hot reserve to be used in case of a failure of one or more of the operating power units.
In these types of systems, optimum conditions are obtained when the total current absorbed by the load is equally supplied by the n elementary units, that is when each power unit supplies a current I having a value of It/n.
Furthermore, it must be noticed that when the power units are comprised of inverters, besides the optimization problems as described above, further new technical problems occur in connection with the phase relationship of the oscillations that are supplied by each inverter. In fact, an inverter is constituted by a unit that is designed to receive a continuous voltage on its input and the inverter is adapted to deliver a sinusoidal voltage to the output so that the frequency of the inverter normally coincides with the frequency of the electrical power distribution line.
The inverters of the previous generation are characterized by the fact that they present an output impedance that does a not have an excessively low value. Consequently, the problems relating to an equal power distribution as described above can be solved through slow control adjustment systems.
On the other hand, modern generation inverters are configured to approximate an ideal voltage generator and are consequently characterized in that they have a particularly low output impedance. The low impedance values result from the use of means that are designed to act in such a manner that the oscillations generated by the inverters have the same level and phase at any time. In fact, if the power system is constituted by n elementary units, having one unit which supplies an oscillation that is shifted in phase with respect to the oscillations generated by the further n-1 units, the power delivered by the n-1 units is delivered to the unit that is out of phase. Consequently possible damage to the unit may be caused the power supplied to the load may be reduced. CL SUMMARY OF THE INVENTION
Therefore, the basic technical problem of the present invention is how to realize a supply system with a monitoring circuit that is particularly fast for allowing level and phase variations in the oscillations, generated by each inverter, in a time as short as possible. A short time will minimize the duration of the negative effects caused by a possible phase shift as described above and will consequently avoid the danger of any damage. The Purpose of the embodiments in the present application is to solve the aforementioned technical problem through the use of circuitry that is particularly simple and economical.
For this purpose and according to the present embodiments of the supply system is of the type comprising n elementary power units, that are connected in parallel to each other with each having control and selective breakaway means.
The monitoring circuit includes the presence of the following characteristic elements:
First means, designed to receive a first signal on their input, that is proportional to the current supplied by the relevant power unit. Also a second signal that is proportional to the average current value is supplied by the n power units and is adapted to calculate the entity of an error signal corresponding to the difference between the first signal and the second signal;
Second means, designed to algebraically add the error signal at the output of the first means to a third signal. The value of the third signal is proportional to the voltage that is supplied by the relevant power unit. Furthermore, the second means is designed to send the third signal, obtained as described above, to the control and selective breakaway means.
The control means modifies the level of the signal relevant power unit until the error signal is cancelled. On the other hand, the selective breakaway means switched off the relevant power unit from the parallel connection when the signal that is supplied by the second means deviates from a nominal value by a predetermined entity.